Category calendar php

<?php
$_SERVER[ 'HTTP_HOST' ] = 'localhost';
$wp_load_loc = "../../../wp-load.php";
require_once($wp_load_loc);
global $post;
global $wpdb;

    function get_calendar_by_category($cat, $current_year = null, $current_month = null){
        global $post;
        global $wpdb;

        $days_in_month = cal_days_in_month(CAL_GREGORIAN, date("n"), date("Y"));

        if(!$current_year){$current_year = date("Y");}else{
            $days_in_month = cal_days_in_month(CAL_GREGORIAN, $current_month, $current_year);
        }
        if(!$current_month){$current_month = date("n");}else{
            $days_in_month = cal_days_in_month(CAL_GREGORIAN, $current_month, $current_year);
        }

        if($current_month == 1){
            $prev_month = 12;
            $prev_year = ($current_year - 1);
        }else{
            $prev_month = ($current_month - 1);
            $prev_year = $current_year;
        }

        if($current_month == 12){
            $next_month = 1;
            $next_year = ($current_year + 1);
        }else{
            $next_month = ($current_month + 1);
            $next_year = $current_year;
        }

        $args = array(
            'cat' => $cat,
            'posts_per_page' => -1,
            'post_type' => 'post',
            'post_status' => 'publish',
            'year' => $prev_year,
            'monthnum' => $prev_month
        );

        $check_prev_month_for_posts = query_posts( $args );
        $check_prev_month_for_posts_count = count($check_prev_month_for_posts);

        if($check_prev_month_for_posts_count){
            $prev_button = "<div id = 'calendar_toggle_prev' onclick = 'get_calendar(" . $prev_year . ", " . $prev_month . ");'><<</div>";
        }else{
            $prev_button = "";
        }

        wp_reset_query();

        $args = array(
            'cat' => $cat,
            'posts_per_page' => -1,
            'post_type' => 'post',
            'post_status' => 'publish',
            'year' => $next_year,
            'monthnum' => $next_month
        );

        $check_next_month_for_posts = query_posts( $args );
        $check_next_month_for_posts_count = count($check_next_month_for_posts);

        if($check_next_month_for_posts_count){
            $next_button = "<div id = 'calendar_toggle_next' onclick = 'get_calendar(" . $next_year . ", " . $next_month . ");'>>></div>";
        }else{
            $next_button = "";
        }

        wp_reset_query();

        $calendar = "";
        $calendar .= "<table class = 'category_calendar'>";
        $calendar .= "<thead><tr><td colspan = '7'><span class = 'underline_this'>" . $prev_button . $next_button . date( 'F', mktime(0, 0, 0, $current_month) ) . ' - ' . $current_year . "</span></td></tr></thead>";
        $calendar .= "<tbody><tr>";

            for($a = 0; $a <= 34; $a++){
                if($a % 7 == 0){
                    $next_row = true;
                }

                if($next_row){
                    $calendar .= "</tr><tr>";
                }

                    $calendar .= "<td>";
                            if($a != 0 && $a <= $days_in_month){

                                $args = array(
                                    'cat' => $cat,
                                    'posts_per_page' => -1,
                                    'post_type' => 'post',
                                    'post_status' => 'publish',
                                    'year' => $current_year,
                                    'monthnum' => str_pad($current_month, 2, "0", STR_PAD_LEFT),
                                    'day' => str_pad($a, 2, "0", STR_PAD_LEFT)
                                );

                                $check_day_for_posts = query_posts( $args );

                                $title_tag = "";

                                foreach( $check_day_for_posts as $post ) :  setup_postdata($post);
                                     $title_tag .= htmlspecialchars(get_the_title(), ENT_QUOTES) . ", ";
                                endforeach;

                                if($title_tag){
                                    $styling = "class = 'active_day'";
                                    $link = "<a $styling title = '" . $title_tag . "' href = '" . get_bloginfo('url') . "/" . $current_year . "/" . str_pad($current_month, 2, "0", STR_PAD_LEFT) . "/" . str_pad($a, 2, "0", STR_PAD_LEFT) . "/'>";
                                    $end = "</a>";
                                }else{
                                    $styling = "";
                                    $link = "";
                                    $end = "";
                                }

                                $calendar .= $link . "<span>" . $a . "</span>" . $end;


                                wp_reset_query();
                            }
                        $calendar .= "</td>";

                $next_row = false;
            }

        $calendar .= "</tbody></tr></table>";

        return $calendar;
    }

    if($_GET["the_year"]){
        $the_year = $_GET["the_year"];
    }else{
        $the_year = null;
    }

    if($_GET["the_month"]){
        $the_month = $_GET["the_month"];
    }else{
        $the_month = null;
    }
    echo get_calendar_by_category(8, $the_year, $the_month);
?>